1. Field of Invention
This invention relates to the field of quality control of manufactured items, and, more particularly, to the detection of faults in the production of articles, such as injection molded plastic cups, glasses, containers, lids or the like, by means of apparatus for sensing light (or similar radiations possibly outside the visible spectrum) transmitted through or/and reflected from the article being inspected and for automatically controlling electrical output signals correlated with the intensity of the radiations sensed in such manner that a predetermined amount of change in the level of such signals will indicate the detection of production faults, such as cracks, "flashes," "short shots" and "grease" deposits.
In a more specific sense, however, the invention provides improved apparatus of the mentioned class, which is adopted for reliably responding in a consistent member (i.e., with substantially equivalent electrical output signals) to either increases or decreases in the level of light being sensed from the article being inspected, which in turn further renders it practical to utilize sensor arrangements best suited for detecting various types of faults in diverse types of articles.
2. Description of the Prior Art
It is known that molded articles, such as cups, glasses, containers or the like, and especially those made from plastic materials by injection molding techniques, are subject to various defects or faults during the manufacturing process, particularly cracks in the walls thereof, so-called "flashes" of extra material or typically irregularly shaped areas of undesired excess thickness either adjacent the rim or elsewhere, so-called "short shots" or unintended voids typically in the form of irregularly shaped notches along the rim, and undesired deposits of foreign materials typically in the nature of spots of "grease" or the like upon the walls.
The earliest approach to quality control in the production of such articles involved visual inspection and manual discarding of defective articles by human inspectors; however, that approach proved both relatively unreliable and much too slow to keep up with the rate at which such articles could be fabricated by injection molding techniques. Accordingly, the need was recognized for providing some form of automated and relatively high speed means for detecting the various types of faults that may occur in the production of the mentioned kind of articles and for eliminating those articles determined to be defective from a batch or stream of same to be accepted as meeting desired quality standards.
Known prior proposals or efforts to provide automated testing of the mentioned kind of articles for production defects are illustrated by the Fouse et al. U.S. Pat. No. 3,067,872, the Powers U.S. Pat. No. 3,557,950, and equipment previously made and marketed substantially in accordance with the disclosure of now abandoned U.S. application Ser. No. 48,694 of Carson et al. filed June 14, 1979, to which the reference is made. From the foregoing and our general knowledge of the state of the art, we regard as previously known and do not herein claim as such the broad concept of automated testing for defects of articles such as injection molded plastic cups or the like, the provision of some suitable means implemented by belts, air flow, vibration or other conveying techniques for successively moving articles to be checked to a testing station or zone, the provision of "feeler" or photoelectric means for sensing when an article has been positioned at such station or zone and is ready for testing, the use of mechanical "feeler" means for detecting short shot type defects, the use in general of various arrangements of light sources and photoelectric sensors for sensing variations of the level of light transmitted through or reflected from the article as indicative of various types of defects such as cracks, flashes or grease deposits, the provision of some suitable means for rotationally or otherwise translating the relative positions of the article being tested and the sensors in order to scan various portions of the article in which defects might occur, the provision in general of some suitable means for producing fault indicating electrical control signals in response to light intensity sensings representing a defect, and the provision of some suitable means adapted to respond to such control signals for separating articles detected as having defects from those which were tested to be of acceptable quality.
Prior article testing systems of this general type typically have included a plurality of light intensity sensors, either for the purpose of providing for the detection of different kinds of defects in the article or in order to provide some desired degree of redundancy in the defect detecting functions. Typically, however, known prior systems of such type have been characterized by either a lack of versatility in reliably detecting the various types of faults that may be encountered or relative complexity of the arrangements of sensors and associated electrical circuitry required or both. It has been recognized that such limitations and disadvantages of known prior systems of such type essentially arose from the facts that different types or occurrences of defects will affect the intensity of the light being sensed in differing ways and such effects will also vary or even be reversed by whether transmitted or reflected light is being sensed, together with the tacit assumption in the design of such prior testing systems that either such system or the portions thereof associated with particular sensors would need to be based upon selection of the fault-indicating criterion as being either an increase in light intensity sensed or a decrease in light intensity being sensed, rather than either of those effects in the alternative. This, in turn, effectively became the working assumption in defining such prior systems by virtue of the fact that the electrical circuits being employed in conjunction with the sensors for providing a fault-indicating electrical output in response to a change in the intensity of light being sensed were adapted for effectively responding to a change in the intensity of the sensed light in only a single direction of increase or decrease therein. As a result of such prior approaches and constraining assumptions in connection with the design of prior testing systems of the general type mentioned, those earlier systems have not been well adapted for employment in testing applications in which it may be desirable to use either transmitted light or reflected light or both, nor to reliable testing for all of the types of defects of interest, and it was apparently further assumed by those working in this field, insofar as we are aware, that greater reliability and versatility in such systems would be achievable only through expensive and relatively much more complex arrangements of sensors and associated electrical circuitry of types not really practical for normal quality control applications.